[USACO12MAR]摩天大楼里的奶牛Cows in a Skyscraper

[USACO12MAR]摩天大楼里的奶牛Cows in a Skyscraper

题目描述

给出n个物品，体积为w[i]，现把其分成若干组，要求每组总体积<=W，问最小分组。(n<=18)

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n,w,a[20],f[300010],g[300010];
int read()
{
    int n=0,f=1;char c=getchar();
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
    while(c>='0'&&c<='9'){n=n*10+c-'0';c=getchar();}
    return n*f;
}
int main()
{
    n=read(),w=read();
    for(int i=1;i<=n;++i)a[i]=read();
    memset(f,0x3f,sizeof(f));
    g[0]=w;
    f[0]=1;
    for(int i=0;i<(1<<n);++i)
        for(int j=1;j<=n;++j)
        {
            if(i&(1<<(j-1)))continue;
            if(g[i]>=a[j]&&f[i|(1<<(j-1))]>=f[i])
            {
                f[i|(1<<(j-1))]=f[i];
                g[i|(1<<(j-1))]=max(g[i]-a[j],g[i|(1<<(j-1))]);
            }
            if(g[i]<a[j]&&f[i|(1<<(j-1))]>=f[i]+1)
            {
                f[i|(1<<(j-1))]=f[i]+1;
                g[i|(1<<(j-1))]=max(w-a[j],g[i|(1<<(j-1))]);
            }
        }
    printf("%d",f[(1<<n)-1]);
    return 0;
}